Ecological Significance of C4 in Plants

C4 cycle which is also called as Hatch and Slack cycle is one of the photosynthetic processes of carbon fixations in plants. CO2 from atmosphere is fixed by enzyme PEP carboxylase, which results in the formation of 4-carbon compound oxaloacetate and hence called as C4 cycle. Plants having C4 cycle are mainly of tropical and sub-tropical regions and are able to survive in environment with low CO2 concentration. Most C4 species are monocots, especially grasses and sedges, although more than 300 are dicots. The anatomy of a C4 is also called as Krantz anatomy because of the presence of radially arranged cells of bundle sheath around their vascular bundle which look like a ring or Wreath (Krantz in German means Wreath).

C4 plants are partially adapted to drought conditions. Photosynthesis is more efficient at high temperature, whereas optimum temperature is much lower. Such high temperature of C4 is due to the stability of enzymes like PEP carboxylase. Oxygen has no inhibitory effect on C4 cycle since PEP carboxylase is insensitive to O2 and photorespiration is absent. Due to absence of photorespiration, CO2 Compensation Point C4 is lower than that of C3 plants. C4 photosynthesis is an adaptation of the C3 pathway that overcomes the limitation of the photorespiration, improving photosynthetic efficiency and minimizing the water loss in hot, dry environments (Edwards & Walker, 1983). Today, C4 plants represent about 5% of Earth’s plant biomass and 1% of its known plant species. Despite this scarcity, they account for about 30% of terrestrial carbon fixation (Osborne and Beerling, 2006). Increasing the proportion of C4 plants on earth could assist Biosequestration of CO2 and represent an important climate change avoidance strategy.

References:
Edwards, G.E. & Walker, D.A. (Eds.) (1983) C3,C4 mechanisms, and cellular and environmental regulation of photosynthesis, Blackwell Scientific, Oxford.
Osborne, C.P.; Beerling, D.J. (2006). “Nature’s green revolution: the remarkable evolutionary rise of C4 plants”. Philosophical Transactions of the Royal Society B: Biological Sciences. 361 (1465): 173–194.

By – Dr. Neha Tiwari Joshi
Department of Botany
Uttaranchal (P.G.) College Of Bio-Medical Sciences & Hospital